Elastomeric pitch lock restraint

Abstract

An exemplary pitch lock for a tiltrotor aircraft to enable and disable a pitching degree of freedom of a rotor blade assembly includes a first tab coupled to a blade stop assembly, the first tab having a first ramp surface, a second tab coupled to a blade cuff, the second tab having a second ramp surface, a hasp having a central opening to receive the first and the second tab and rollers rotatably coupled to the hasp on opposite sides of the central opening, where the rollers engage the first and second ramp surfaces and retain the first and the second tabs in the central opening.

What is claimed is: 
     
       1. A pitch lock for a tiltrotor aircraft to enable and disable a pitching degree of freedom of a rotor blade assembly, the pitch lock comprising:
 a first tab coupled to a blade stop assembly, the first tab having a first ramp surface; 
 a second tab coupled to a blade cuff, the second tab having a second ramp surface; 
 a hasp having a central opening to receive the first and the second tab; and 
 rollers rotatably coupled to the hasp on opposite sides of the central opening, wherein the rollers engage the first and second ramp surfaces and retain the first and the second tabs in the central opening. 
 
     
     
       2. The pitch lock of  claim 1 , wherein the first and second ramp surfaces each comprise a recess, wherein the rollers are positioned in the recesses when in a pitch locked position. 
     
     
       3. The pitch lock of  claim 1 , wherein each of the rollers comprises an inner sleeve having a bore;
 an outer sleeve; and 
 an elastomeric material disposed between the inner sleeve and the outer sleeve. 
 
     
     
       4. The pitch lock of  claim 3 , wherein the inner sleeve and the outer sleeve are constructed of a metal. 
     
     
       5. The pitch lock of  claim 3 , wherein the bore disposes an axle and the bore comprises a low-friction liner. 
     
     
       6. The pitch lock of  claim 1 , wherein the first and the second ramp surfaces are sloped outward toward the rollers from a first point to a maximum deflection point, whereby the rollers are deformed as they move from the first point to the maximum deflection point to load the first and the second tabs together. 
     
     
       7. The pitch lock of  claim 6 , wherein each of the rollers comprises an inner sleeve having a bore;
 an outer sleeve; and 
 an elastomeric material disposed between the inner sleeve and the outer sleeve. 
 
     
     
       8. The pitch lock of  claim 6 , wherein the first and second ramp surfaces further comprise a recess located on an opposite side of the maximum deflection point from the first point. 
     
     
       9. The pitch lock of  claim 8 , wherein each of the rollers comprises an inner sleeve having a bore;
 an outer sleeve; and 
 an elastomeric material disposed between the inner sleeve and the outer sleeve. 
 
     
     
       10. The pitch lock of  claim 9 , wherein the inner sleeve and the outer sleeve are constructed of a metal; and
 the bore disposes an axle and the bore comprises a low-friction liner. 
 
     
     
       11. A tiltrotor aircraft having rotary and non-rotary flight modes, the tiltrotor aircraft comprising:
 a rotor assembly having a gimballing degree of freedom relative to a mast, the rotor assembly including a plurality of rotor blade assemblies each having a pitching degree of freedom and a folding degree of freedom; 
 a gimbal lock positioned about the mast, the gimbal lock having a disengaged position relative to the rotor assembly enabling the gimballing degree of freedom in the rotary flight mode and an engaged position relative to the rotor assembly disabling the gimballing degree of freedom in the non-rotary flight mode; 
 a blade stop assembly positioned about the mast, the blade stop assembly including a plurality of arms having a radially contracted orientation in the rotary flight mode and a radially extended orientation in the non-rotary flight mode; and 
 a pitch lock in a pitch locked position disabling a pitching degree of freedom of the respective rotor blade assembly in the non-rotary flight mode, the pitch lock comprising: 
 a first tab of the arm of the respective rotor blade assembly having a first ramp surface; 
 a second tab of blade cuff having a second ramp surface; 
 a hasp having a central opening to receive in the pitch locked position the first tab and the second tab; 
 rollers rotatably coupled to the hasp on opposite sides of the central opening, wherein the rollers engage the first and second ramp surfaces and retain the first and the second tabs in the central opening; and 
 wherein the first and the second ramp surfaces are sloped outward toward the rollers from a first point to a maximum deflection point, whereby the rollers are deformed as they move from the first point to the maximum deflection point to load the first and the second tabs together. 
 
     
     
       12. The tiltrotor aircraft of  claim 11 , wherein the first and second ramp surfaces each comprise a recess, wherein the rollers are positioned in the recesses when in a pitch locked position. 
     
     
       13. The tiltrotor aircraft of  claim 11 , wherein each of the rollers comprises an inner sleeve having a bore;
 an outer sleeve; and 
 an elastomeric material disposed between the inner sleeve and the outer sleeve. 
 
     
     
       14. The tiltrotor aircraft of  claim 13 , wherein the first and second ramp surfaces further comprise a recess located on an opposite side of the maximum deflection point from the first point. 
     
     
       15. A method for enabling and disabling a pitching degree of freedom of a rotor blade assembly of a tiltrotor aircraft, the method comprising:
 rotating a pitch lock from an unlocked position to a pitch locked position, the pitch lock comprising a first tab coupled to a blade stop assembly and having a first ramp surface, a second tab coupled to a blade cuff and having a second ramp surface, a hasp having a central opening, and rollers rotatably coupled to the hasp on opposite sides of the central opening, wherein the first tab and the second tab are located outside of the central opening in the unlocked position and the first tab and the second tab received in the central opening in the pitch locked position; 
 engaging the rollers on the first and the second ramp surfaces as the pitch lock rotates to the pitch locked position; and 
 deforming the rollers in response to engaging the first and the second ramp surfaces thereby preloading the first and the second tab together. 
 
     
     
       16. The method of  claim 15 , further comprising positioning, in the pitch locked position, the rollers in a recess in the respective first and second ramp surfaces. 
     
     
       17. The method of  claim 15 , wherein the first and the second ramp surfaces are sloped outward toward the rollers from a first point to a maximum deflection point. 
     
     
       18. The method of  claim 17 , further comprising positioning, in the pitch locked position, the rollers in a recess in the respective first and second ramp surfaces, wherein the recess is located on an opposite side of the maximum deflection point from the first point. 
     
     
       19. The method of  claim 15 , wherein each of the rollers comprises an inner sleeve having a bore disposing an axle;
 an outer sleeve; and 
 an elastomeric material disposed between the inner sleeve and the outer sleeve. 
 
     
     
       20. The method of  claim 19 , wherein the first and the second ramp surfaces are sloped outward toward the rollers from a first point to a maximum deflection point; and
 further comprising positioning, in the pitch locked position, the rollers in a recess in the respective first and second ramp surfaces, wherein the recess is located on an opposite side of the maximum deflection point from the first point.